The same applies to roughly one-third of heavy commercial vehicles, which have often been certified under far more lenient standards despite the far higher annual mileage each one covers compared to a passenger vehicle.

The summary that opens the Nature article contains the following points:

Regulated NOx emission limits in leading markets have been progressively tightened, but current diesel vehicles emit far more NOx under real-world operating conditions than during laboratory certification testing

These excess emissions (totaling 4.6 million tons) are associated with about 38,000 ... premature deaths globally in 2015, including about 10 percent of all ozone-related premature deaths in the 28 European Union member states.

Heavy-duty vehicles are the dominant contributor to excess diesel NOx emissions and associated health impacts in almost all regions.

Nitrogen oxides, the study notes, are key precursors to the formation of both ozone and specific types of particulate matter (known as PM2.5).

The final set of Euro 6 standards are roughly equivalent to those in effect in the U.S. for passenger vehicles since January 2008, known as "Tier 2 Bin 5."

Significantly, the study concludes that all but eliminating real-world NOx emissions from diesels, hence averting 174,000 premature deaths, "can be achieved by implementing Euro VI standards" for all vehicles not yet covered by them.

In other words, bring new heavy-duty trucks to the same emission standards as cars must now meet in Europe and North America, and replace older trucks with newer ones, and by 2040, NOx emissions from diesel engines will largely have been eliminated as a public-health menace.

That was, arguably, the point of many earlier limits on diesel emissions.

Which two-thirds of diesel passenger vehicles didn't actually meet when used in the real world.

EDITOR'S NOTE: An earlier version of this story said the Diesel Technology Forum replied to the study described before it hit the media. In fact, the lobbying group issued its statement more than five hours after the study was released—and after it had been covered by The New York Times. The story has been updated; we apologize for the error.